This invention relates to hypodermic syringes and more particularly to a hypodermic syringe assembly which can be used only once to load and discharge a fluid, the process of discharging acting to render the assembly non-usable, and to a lockable needle cap which may be locked over the needle after the syringe has been used.
With the increase of drug addiction by the intravenous injection of drugs in today's society, and the growth of certain health destroying diseases such as hepatitis and AIDS, which can be transmitted by the multiple use of syringes, it is highly desirable that hypodermic syringes be used only once and either destroyed or discarded in such a state that they are not reusable. Separate devices for destroying a syringe after use involves severing the needle and barrel components and results in the inconvenience of the additional acts of placing the syringe in the device and activating such device. If the syringe is not immediately destroyed in such a device but awaits personel to perform the act, the syringe may escape the normal procedure and be displaced before destruction can occur. Thus, a substantial number of non-reusable syringes have been proposed in the art in recent years.
In preparation for this application a preexamination patentability search was conducted and located the following U.S. Pat. Nos. 4,233,795 (Yerman); 4,391,272 (Staempfli); 4,713,056 (Butterfield); 4,731,068 (Hesse); 3,890,971 (Leeson et al); 4,650,468 (Jennings); 4,675,005 (DeLuccia); 4,687,467 (Cygielski); and 4,121,588 (Geiger).
In Yerman '975 there is a blocking member which is engaged by a plunger to close the fluid compartment after one use, the plunger not being connected to the blocking member so that on subsequent withdrawal of the plunger, the blocking member cannot be moved. In Staempfli '272 the plunger has a separable body which can move in one direction and thereafter lock and disconnect when the plunger is pulled back to the original position. In Hesse '068 there is a spider attached to a rod which is fastened to the plunger, the spider acting to pull a slidable sleeve rearwardly during the load stroke and to slip past the sleeve during the ejection stroke, the tips of the spider grasping the wall of the syringe thereafter to prevent further retraction of the plunger. In Butterfield '056 there is a latch ring which grasps the plunger head after the plunger has completed the ejection stroke thereby to prevent the plunger from again being retracted. In Jennings '468 the piston head housing is releasably locked to the syringe barrel and after injection it is unlocked by twisting and retracted together with the needle to the opposite end of the barrel where it is automatically locked against further use. In Leeson et al '971 there is a plunger and needle cap which may be permanently locked after use. In DeLuccia '005 there is a tool attached to the end of the plunger which can engage and withdraw the cannula and needle into the body of the syringe, and when in the body upon rotation, the rear of the piston can be threadedly locked to the closed end of the syringe body. Cygielski '467 has an internal cutter which punctures a hole in the needle end of the piston to prevent reuse, while Gieger '588 has a weakened zone for breaking of the barrel of the syringe.
One of the problems with all of the known prior art is that during the discharge portion of the cycle, if the plunger is not pushed far enough to inject all of the fluid through the syringe, the plunger may yet be pulled back and the syringe reused. Thus, if one who is using the syringe inadvertently does not push the plunger all the way during the discharge stroke, the syringes are not rendered inoperative.